1. Field of the Invention
This invention relates to substrates for interconnecting electronic integrated-circuit components, and more particularly to an arrangement for repairing the electrical circuits which are carried by such substrates.
2. Description of the Prior Art
Modern techniques currently employed to produce electronic equipment, and more particularly data-processing assemblies, are making increasing use of integrated circuit semiconductor devices referred to as integrated circuit chips. They are generally rectangular in shape and are provided along at least one side with output conductors.
Such integrated circuit chips may be interconnected by substrates as is well known. These substrates are generally made of an insulating material provided with connecting conductors produced in the form of circuits printed on a plate. The conductors are usually divided into a plurality of layers which are separated by insulating layers and which are connected together by through-connectors, the latter being formed by openings made in the insulating layers and which are filled with a conductive material so as to make connections between conductive layers lying one above the other. The outermost conductive layer of the multi-layer interconnecting substrate is provided with connecting contacts bordering at least one location or site on the substrate, these sites being intended to receive an electronic component such as an integrated circuit chip. For an example of integrated circuit chips being mounted on an interconnecting substrate, reference may be made to the applications of Raymond Delorme et al, Ser. Nos. 801,787 now U.S. Pat. No. 4,116,376 and 874,652 directed to a method and apparatus for mounting chip devices on a substrate, were filed in the United States Patent and Trademark Office on May 31, 1977 and Feb. 2, 1978, respectively, and which are assigned to the assignee of the present invention.
In view of the fact that the through openings formed in the outermost insulating layer (which is the uppermost insulating layer of the substrate), which are intended to allow connections to the contacts around a site to be made, are aligned with conductors in conductive layers internal to the interconnecting substrate, and bearing in mind the high density of conductors required in a substrate for the purposes of miniaturization, it will be readily appreciated that the position of each of these openings is confined to a narrow zone of tolerance. The result is that the through openings can only be situated inside or outside a site, at which the electronic component or chip is situated.
Modification or repair of interconnecting substrates is often done in design laboratories. In such laboratories, technicians work with highly elaborate substrates and frequently find it necessary or advantageous to modify the interconnecting circuits of the substrate. Such modifications are called for in a number of cases, particularly when "breadboarding" or testing new circuit designs. For example, it may be necessary to isolate the connection to at least one contact connected to a component; to connect a contact to part of the substrate; to isolate a connection to a contact so that the isolated connection or the contact can be connected to another part of the substrate; and to insert a new connection to connect two separate parts of the substrate, such as two contacts associated with the same site or two separate sites. To sum up, to make alterations, it is necessary or advantageous to isolate a connection and/or add another connection to the given substrate. The isolating is done with an instrument which severs the connection, while the additional connection requires the introduction of an additional conductor into the substrate and the soldering of its two ends to the parts of the substrate to be connected.
The use of the isolating instrument and of instruments for guiding the additional conductor and for soldering its ends is only feasible if the repair zone is satisfactorily exposed. This is the case when the contact concerned is attached to a through-connection outside the site where the chip is situated. If on the other hand the through-connection is inside the site, it is necessary for the component to be removed and, in the case of making an additional connection, for this connection to be passed under and between the output conductors of the component so that it can be attached outside the site. There are many disadvantages in doing this.
Firstly, removing the component and replacing it after repair are operations calling for great care which are responsible for a considerable increase in the repair time, or indeed in the loss of the component, which makes it a remarkably expensive undertaking. Then, as regards the actual operation itself, it is necessary again to make use of an apparatus for mounting integrated circuit devices on a substrate (such as the apparatus which is described in the aforenoted patent application Ser. No. 801,787) in order to fit the component, while allowing for the additional connection which has to pass under and between the output conductors of the component. Finally, and particularly from the point of view of the use, the reliability of such repairs are always in question because of all the risks of short-circuits between, on the one hand, the soldered joint of the inner end of the additional connection and the output conductors of the component, and on the other hand, the additional connection itself and the output conductors of the component.
The subject invention provides a repair arrangement which does not suffer from the above mentioned disadvantages of prior art repair arrangements.